Doubling decimal numbers

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Students learn to double decimal numbers.

CCSS.Math.Content.5.NBT.B.7

Students will be able to double decimal numbers.

Show the numbers on the interactive whiteboard. In the lower row are the numbers that are the double of the numbers in the higher row. Have the students state which numbers belong together and draw a line between these numbers. Ask how the students calculated this.

You explain that doubling is exactly two times the value that you already have. Drag the piggy bank with $7.20 away to show visually that you then have double the amount. Next you show the different methods you can use to calculate the double. You can multiply it by two or you can add the same number again. Have the students practice doubling by calculating the double of the numbers on the interactive whiteboard. Then the students fill in a chart, in which they must fill in the double of each number in the chart. Have the students describe which method they used to calculate their answers. For this you can multiply the number by two or add it two times.

Check whether the students can double decimal numbers by asking the following questions:

Why is it useful to be able to double?

What do you always do if you need to calculate the double of a number?

What is the double of 42.6?

Students test their understanding of doubling decimal numbers through ten exercises. For some of these they must provide the double of the given number. In other exercises, they must fill in a doubles chart. One exercises has a number with two decimal places.

You discuss once again with the students that it is important to be able to double, because that is how you can calculate the answer to a problem more easily. On the whiteboard there are three numbers that the students must double. By removing the covers, they can see the answers. Next you can give the students cards with decimal numbers, on which pairs of cards match each other because one is the double of the other. The students walk around through the class and look for the person with the double of their number, or whose number they have the double of.

When students have difficulty with doubling, you can have them practice with a number line. Have them double the number and draw jumps on the number line.

Cards with decimal numbers and their respective doubles.

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